Multi-field Microphone – when the Sound Field is unknown

Only a small percentage of all acoustical measurements are performed in the welldefined and well-controlled environment of a calibration laboratory – on the contrary most acoustical measurements are done under non-controlled conditions which in many cases are not even known in beforehand. This is the reason that some acoustical standards such as the IEC 61672 series (the “Sound Level Meter standard”) specify the performance of the measuring microphone over a wide range of environmental conditions. Modern quality measuring condenser microphones often meet or exceed the requirements even under very varying conditions. However one important – and unfortunately in many cases major – source of error is often neglected: The response of the actual microphone type in the actual sound field. The influence of different sound fields on the measurement error is discussed in some detail with practical examples and it is shown how a worstcase error exceeding 10 dB @ 20 kHz is a real risk. After a brief discussion of a condenser microphone which drastically reduces the error caused by influence of an unknown sound field or varying angle of incidence. Finally, test results from production samples of the new microphone are shown.